ASTM D5236 Test Method for Distillation of Heavy Hydrocarbon Mixtures (Vacuum Potstill Method)
1. Scope
1.1 This test method covers the procedure for distillation of heavy hydrocarbon mixtures having initial boiling points greater than 150 °C (300 °F), such as heavy crude oils, petroleum distillates, residues, and synthetic mixtures. It employs a potstill with a low pressure drop entrainment separator operated under total takeoff conditions. Distillation conditions and equipment performance criteria are specified and typical apparatus is illustrated.

1.2 This test method details the procedures for the production of distillate fractions of standardized quality in the gas oil and lubricating oil range as well as the production of standard residue. In addition, it provides for the determination of standard distillation curves to the highest atmospheric equivalent temperature possible by conventional distillation.

1.3 The maximum achievable atmospheric equivalent temperature (AET) is dependent upon the heat tolerance of the charge. For most samples, a temperature up to 565 °C (1050 °F) can be attained. This maximum will be significantly lower for heat sensitive samples (for example, heavy residues) and might be somewhat higher for nonheat sensitive samples.

1.4 The recommended distillation method for crude oils up to cutpoint 400 °C (752 °F) AET is Test Method D2892. This test method can be used for heavy crude oils with initial boiling points greater than 150 °C (302 °F). However, distillation curves and fraction qualities obtained by these methods are not comparable.

1.5 This test method contains the following annexes:
1.5.1 Annex A1 - Test Method for Determination of Temperature Response Time,

1.5.2 Annex A2 - Practice for Calibration of Sensors,

1.5.3 Annex A3 - Test Method for Dehydration of a Wet Sample of Oil,

1.5.4 Annex A4 - Practice for Conversion of Observed Vapor Temperature to Atmospheric Equivalent Temperature (AET), and

1.5.5 Annex A5 - Test Method for Determination of Wettage.

1.6 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific warnings, see 6.5.4.2, 6.5.6.3, 6.9.3, 9.5, 9.7, and A2.3.1.3.

1.8 WARNING - Mercury has been designated by many regulatory agencies as a hazardous material that can cause central nervous system, kidney, and liver damage. Mercury, or its vapor, may be hazardous to health and corrosive to materials. Caution should be taken when handling mercury and mercury containing products. See the applicable product Material Safety Data Sheet (MSDS) for details and EPA for additional information. Users should be aware that selling mercury and/or mercury containing products into your state or country may be prohibited by law.

1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

2. Referenced Documents
2.1 ASTM Standards:
D941 Test Method for Density and Relative Density (Specific Gravity) of Liquids by Lipkin Bicapillary Pycnometer (Withdrawn 1993)
D1217 Test Method for Density and Relative Density (Specific Gravity) of Liquids by Bingham Pycnometer
D1250 Guide for Use of the Petroleum Measurement Tables
D1298 Test Method for Density, Relative Density, or API Gravity of Crude Petroleum and Liquid Petroleum Products by Hydrometer Method
D1480 Test Method for Density and Relative Density (Specific Gravity) of Viscous Materials by Bingham Pycnometer
D2892 Test Method for Distillation of Crude Petroleum (15-Theoretical Plate Column)
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
D5002 Test Method for Density and Relative Density of Crude Oils by Digital Density Analyzer

3. Terminology
3.1 Definitions ofTerms Specific to This Standard:
3.1.1 boil-up rate, n - the quantity of vapor entering the distillation head per unit time.
3.1.1.1 Discussion - It is approximately equal to the takeoff rate, differing only by the parasitic heat losses. It is expressed in millilitres per hour for a head of any given internal diameter or millilitres per hour per square centimetre of cross-sectional area of the throat for comparative purposes.

3.1.2 condenser, n - the apparatus connected to the outlet of the distillation head in which condensation of the product occurs.

3.1.3 distillation flask, n - the flask, of glass or metal, in which the charge is boiled.
3.1.3.1 Discussion - The flask is sometimes called a kettle or pot.

3.1.4 distillation head, n - the section immediately above the distillation flask containing the entrainment separator.

3.1.5 distillation pressure (or operating pressure), n - the pressure measured in the distillation head just before the outlet to the recovery system.

3.1.6 distillation temperature (or vapor temperature), n - the temperature of the vapors in the distillation head at the point of measurement.

3.1.7 loading, n - the volume of charge relative to the cross-sectional area of the neck.

3.1.8 pressure drop, n - the difference between the operating pressure and the pressure measured in the distillation flask.
3.1.8.1 Discussion - It is a result of the friction developed by driving the vapors through the system expressed in kilopascals (mm Hg).

3.1.9 spillover point, n - the lowest point in the head above the entrainment separator over which the vapors can flow to the condensing region.

3.1.10 static hold-up (or wettage), n - the amount of liquid material remaining on the inside of the walls of the apparatus after the distillation has been completed.
3.1.10.1 Discussion - In this test method, it includes wettage of the distillation flask in the case of the steel flasks, but not in the case of glass flasks that are removed for weighing after the distillation is completed.

3.1.11 takeoffrate, n - the quantity of product removed per unit time.
3.1.11.1 Discussion - It is approximately equal to the boil-up rate differing only by parasitic heat losses.